### Struct

# GLib Date

#### Description [src]

    struct GDate {
      guint julian_days : 32;
      guint julian : 1;
      guint dmy : 1;
      guint day : 6;
      guint month : 4;
      guint year : 16;
    }

`GDate` is a struct for calendrical calculations.

The `GDate` data structure represents a day between January 1, Year 1, and sometime a few thousand years in the future (right now it will go to the year 65535 or so, but `g_date_set_parse()` only parses up to the year 8000 or so - just count on “a few thousand”). `GDate` is meant to represent everyday dates, not astronomical dates or historical dates or ISO timestamps or the like. It extrapolates the current Gregorian calendar forward and backward in time; there is no attempt to change the calendar to match time periods or locations. `GDate` does not store time information; it represents a day.

The `GDate` implementation has several nice features; it is only a 64-bit struct, so storing large numbers of dates is very efficient. It can keep both a Julian and day-month-year representation of the date, since some calculations are much easier with one representation or the other. A Julian representation is simply a count of days since some fixed day in the past; for `GDate` the fixed day is January 1, 1 AD. (“Julian” dates in the `GDate` API aren’t really Julian dates in the technical sense; technically, Julian dates count from the start of the Julian period, Jan 1, 4713 BC).

`GDate` is simple to use. First you need a “blank” date; you can get a dynamically allocated date from `g_date_new()`, or you can declare an automatic variable or array and initialize it by calling `g_date_clear()`. A cleared date is safe; it’s safe to call `g_date_set_dmy()` and the other mutator functions to initialize the value of a cleared date. However, a cleared date is initially invalid, meaning that it doesn’t represent a day that exists. It is undefined to call any of the date calculation routines on an invalid date. If you obtain a date from a user or other unpredictable source, you should check its validity with the `g_date_valid()` predicate. `g_date_valid()` is also used to check for errors with `g_date_set_parse()` and other functions that can fail. Dates can be invalidated by calling `g_date_clear()` again.

It is very important to use the API to access the `GDate` struct. Often only the day-month-year or only the Julian representation is valid. Sometimes neither is valid. Use the API.

GLib also features `GDateTime` which represents a precise time.

###### Structure members

`julian_days`

  The Julian representation of the date.

`julian`

  This bit is set if `julian_days` is valid.

`dmy`

  This is set if `day`, `month` and `year` are valid.

`day`

  The day of the day-month-year representation of the date, as a number between 1 and 31.

`month`

  The month of the day-month-year representation of the date, as a number between 1 and 12.

`year`

  The year of the day-month-year representation of the date.

#### Constructors

###### g_date_new

Allocates a `GDate` and initializes it to a safe state. The new date will be cleared (as if you’d called g_date_clear()) but invalid (it won’t represent an existing day). Free the return value with g_date_free().

###### g_date_new_dmy

Create a new `GDate` representing the given day-month-year triplet.

###### g_date_new_julian

Create a new `GDate` representing the given Julian date.

#### Functions

###### g_date_get_days_in_month

Returns the number of days in a month, taking leap years into account.

###### g_date_get_monday_weeks_in_year

Returns the number of weeks in the year, where weeks are taken to start on Monday. Will be 52 or 53. The date must be valid. (Years always have 52 7-day periods, plus 1 or 2 extra days depending on whether it’s a leap year. This function is basically telling you how many Mondays are in the year, i.e. there are 53 Mondays if one of the extra days happens to be a Monday.).

###### g_date_get_sunday_weeks_in_year

Returns the number of weeks in the year, where weeks are taken to start on Sunday. Will be 52 or 53. The date must be valid. (Years always have 52 7-day periods, plus 1 or 2 extra days depending on whether it’s a leap year. This function is basically telling you how many Sundays are in the year, i.e. there are 53 Sundays if one of the extra days happens to be a Sunday.).

###### g_date_is_leap_year

Returns `TRUE` if the year is a leap year.

###### g_date_strftime

Generates a printed representation of the date, in a locale-specific way. Works just like the platform’s C library `strftime()` function, but only accepts date-related formats; time-related formats give undefined results. Date must be valid. Unlike `strftime()` (which uses the locale encoding), works on a UTF-8 format string and stores a UTF-8 result.

###### g_date_valid_day

Returns `TRUE` if the day of the month is valid (a day is valid if it’s between 1 and 31 inclusive).

###### g_date_valid_dmy

Returns `TRUE` if the day-month-year triplet forms a valid, existing day in the range of days `GDate` understands (Year 1 or later, no more than a few thousand years in the future).

###### g_date_valid_julian

Returns `TRUE` if the Julian day is valid. Anything greater than zero is basically a valid Julian, though there is a 32-bit limit.

###### g_date_valid_month

Returns `TRUE` if the month value is valid. The 12 `GDateMonth` enumeration values are the only valid months.

###### g_date_valid_weekday

Returns `TRUE` if the weekday is valid. The seven `GDateWeekday` enumeration values are the only valid weekdays.

###### g_date_valid_year

Returns `TRUE` if the year is valid. Any year greater than 0 is valid, though there is a 16-bit limit to what `GDate` will understand.

#### Instance methods

###### g_date_add_days

Increments a date some number of days. To move forward by weeks, add weeks*7 days. The date must be valid.

###### g_date_add_months

Increments a date by some number of months. If the day of the month is greater than 28, this routine may change the day of the month (because the destination month may not have the current day in it). The date must be valid.

###### g_date_add_years

Increments a date by some number of years. If the date is February 29, and the destination year is not a leap year, the date will be changed to February 28. The date must be valid.

###### g_date_clamp

If `date` is prior to `min_date`, sets `date` equal to `min_date`. If `date` falls after `max_date`, sets `date` equal to `max_date`. Otherwise, `date` is unchanged. Either of `min_date` and `max_date` may be `NULL`. All non-`NULL` dates must be valid.

###### g_date_clear

Initializes one or more `GDate` structs to a safe but invalid state. The cleared dates will not represent an existing date, but will not contain garbage. Useful to init a date declared on the stack. Validity can be tested with g_date_valid().

###### g_date_compare

Qsort()-style comparison function for dates. Both dates must be valid.

###### g_date_copy

Copies a GDate to a newly-allocated GDate. If the input was invalid (as determined by g_date_valid()), the invalid state will be copied as is into the new object.

since: 2.56

###### g_date_days_between

Computes the number of days between two dates. If `date2` is prior to `date1`, the returned value is negative. Both dates must be valid.

###### g_date_free

Frees a `GDate` returned from g_date_new().

###### g_date_get_day

Returns the day of the month. The date must be valid.

###### g_date_get_day_of_year

Returns the day of the year, where Jan 1 is the first day of the year. The date must be valid.

###### g_date_get_iso8601_week_of_year

Returns the week of the year, where weeks are interpreted according to ISO 8601.

since: 2.6

###### g_date_get_julian

Returns the Julian day or “serial number” of the `GDate`. The Julian day is simply the number of days since January 1, Year 1; i.e., January 1, Year 1 is Julian day 1; January 2, Year 1 is Julian day 2, etc. The date must be valid.

###### g_date_get_monday_week_of_year

Returns the week of the year, where weeks are understood to start on Monday. If the date is before the first Monday of the year, return 0. The date must be valid.

###### g_date_get_month

Returns the month of the year. The date must be valid.

###### g_date_get_sunday_week_of_year

Returns the week of the year during which this date falls, if weeks are understood to begin on Sunday. The date must be valid. Can return 0 if the day is before the first Sunday of the year.

###### g_date_get_weekday

Returns the day of the week for a `GDate`. The date must be valid.

###### g_date_get_year

Returns the year of a `GDate`. The date must be valid.

###### g_date_is_first_of_month

Returns `TRUE` if the date is on the first of a month. The date must be valid.

###### g_date_is_last_of_month

Returns `TRUE` if the date is the last day of the month. The date must be valid.

###### g_date_order

Checks if `date1` is less than or equal to `date2`, and swap the values if this is not the case.

###### g_date_set_day

Sets the day of the month for a `GDate`. If the resulting day-month-year triplet is invalid, the date will be invalid.

###### g_date_set_dmy

Sets the value of a `GDate` from a day, month, and year. The day-month-year triplet must be valid; if you aren’t sure it is, call `g_date_valid_dmy()` to check before you set it.

###### g_date_set_julian

Sets the value of a `GDate` from a Julian day number.

###### g_date_set_month

Sets the month of the year for a `GDate`. If the resulting day-month-year triplet is invalid, the date will be invalid.

###### g_date_set_parse

Parses a user-inputted string `str`, and try to figure out what date it represents, taking the current locale into account. If the string is successfully parsed, the date will be valid after the call. Otherwise, it will be invalid. You should check using `g_date_valid()` to see whether the parsing succeeded.

###### g_date_set_time

Sets the value of a date from a `GTime` value. The time to date conversion is done using the user’s current timezone.

deprecated: 2.10

###### g_date_set_time_t

Sets the value of a date to the date corresponding to a time specified as a time_t. The time to date conversion is done using the user’s current timezone.

since: 2.10

###### g_date_set_time_val

Sets the value of a date from a `GTimeVal` value. Note that the `tv_usec` member is ignored, because `GDate` can’t make use of the additional precision.

deprecated: 2.62 since: 2.10

###### g_date_set_year

Sets the year for a `GDate`. If the resulting day-month-year triplet is invalid, the date will be invalid.

###### g_date_subtract_days

Moves a date some number of days into the past. To move by weeks, just move by weeks*7 days. The date must be valid.

###### g_date_subtract_months

Moves a date some number of months into the past. If the current day of the month doesn’t exist in the destination month, the day of the month may change. The date must be valid.

###### g_date_subtract_years

Moves a date some number of years into the past. If the current day doesn’t exist in the destination year (i.e. it’s February 29 and you move to a non-leap-year) then the day is changed to February 29. The date must be valid.

###### g_date_to_struct_tm

Fills in the date-related bits of a struct tm using the `date` value. Initializes the non-date parts with something safe but meaningless.

###### g_date_valid

Returns `TRUE` if the `GDate` represents an existing day. The date must not contain garbage; it should have been initialized with `g_date_clear()` if it wasn’t allocated by one of the `g_date_new()` variants.